The present invention relates to an air conditioning system for a vehicle, and more particularly to a vehicle air conditioning system capable of providing continuous and smooth air conditioning.
Vehicle air conditioning systems are divided broadly into the reheat type and the air mix type. In the reheat type intake air is first cooled, and then heated to a desired temperature by a heater. In the air mix type, the desired air temperature is attained by varying the mixing ratio between cool air and hot air. However, there is little difference between the two types with respect to control method.
FIG. 6 shows one conventional automatic vehicle air conditioning system belonging to the air mix type.
The air conditioning system of FIG. 6 includes a control unit 1 composed of electrical circuits, a sensor 2 for sensing the temperature of inside air in the interior of the vehicle, a sensor 3 for sensing the temperature of outside ambient air, a sensor 4 for sensing the temperature of engine cooling water, and a sunshine output 5. Sensor signals of the sensors 2-5 are input to the control unit 1.
A conditioning equipment 6 includes an intake door 7 for adjusting the amount of incoming air from the inside or outside of the vehicle, a blower 9 driven by a blower motor 8, and an air mix door 12 for adjusting the amount of air passing through a heater 11. The position of the air mix door 12 is controlled by a door position control servo 10. The air conditioning equipment 6 further includes a defroster door 13 for adjusting the amount of air supplied to a defroster, a foot door 14 for adjusting the amount of air discharged toward the feet of occupants, and a ventilator door 15 for adjusting the amount of air supplied to a ventilator. The air mix door 12 is disposed between an inlet side on which the intake door 7 is provided, and an outlet side on which the defroster door 13, foot door 14 and ventilator door 15 are provided.
In this air conditioning system, the control unit 1 is arranged to perform feedback control based on the output signal of the inside temperature sensor 2 for controlling the inside temperature toward a desired temperature or a preset temperature, and a feed-forward control based on the output signals of the outside temperature sensor 3 and the sunshine sensor 5 so as to satisfy a predetermined thermal equilibrium condition. The control unit 1 sends control signals to the blower motor 8 and the door position control servo 10.
When rapid acceleration of the vehicle or a high load is detected by a vacuum switch 16 for sensing an intake manifold negative pressure in an engine system, a timer 17 is actuated. While the timer 17 is operative, a compressor clutch 18 is disengaged, and accordingly an air conditioning compressor 19 is held inoperative to give priority to the running performance of the vehicle.
In this conventional system, however, the timer 17 is operated intermittently, the fine adjustment of cut-off duration for interrupting the compressor is difficult and possible only in a narrow range, and information about the inside temperature is not used in determining the cut-off duration. Therefore, this conventional system tends to allow a sharp increase in the inside temperature especially when rapid acceleration or high load operation is continued in summer, by failing to maintain an adequate balance between the running performance of the vehicle, and the performance in air conditioning. Even though a microcomputer or other complicated circuitry is employed to optimize the control of the air conditioning, the tuning process during initial adjustment is troublesome and time-consuming because the number of control parameters is large.